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Sum of subsets /= sum of whole??

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Sam
Sam 2014-11-14
评论： Sam 2014-11-14
I have a MATfile (attached) containing a 3-dimensional array of size [90 144 120]. The array is called ba_lm3. If I subset the array into two equally-sized halves, the sum of all values in each of those halves is different from if I sum all values in the original array. Take a look:
>> sum(ba_lm3(:))
ans =
46601836
>> sum(sum(sum(ba_lm3(:,73:144,:)))) + sum(sum(sum(ba_lm3(:,1:72,:))))
ans =
46604364
The 2nd (subsetted) dimension of the sub-arrays is indeed 72+72=144:
>> size(ba_lm3(:,73:144,:))
ans =
90 72 120
>> size(ba_lm3(:,1:72,:))
ans =
90 72 120
>> size(ba_lm3)
ans =
90 144 120
And I don't think there should be any overlap.
I have observed this problem on machines running MATLAB r2009b and r2013b, so I think it must either be a problem with my code or the array. Any ideas?
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Azzi Abdelmalek
Azzi Abdelmalek 2014-11-14
Your problem is not clear
James Tursa
James Tursa 2014-11-14
What is the class of ba_lm3?

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采纳的回答

Azzi Abdelmalek
Azzi Abdelmalek 2014-11-14
编辑：Azzi Abdelmalek 2014-11-14
a_lm3 is a single array, if you want to get the same result
ba_lm3=double(ba_lm3);
a=ba_lm3(:,1:72,:);
b=ba_lm3(:,73:144,:);
s1=sum(ba_lm3(:))
s2=sum(a(:))+sum(b(:))

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